Graph API Throttling Request Headers Priority : x-ms-throttle-priority

Question

I am trying to set the priority for each request in my application as mentioned in this docs: https://learn.microsoft.com/en-us/graph/throttling

As per the docs:

Note: Should requests be throttled, low priority requests will be throttled first, normal priority requests second, and high priority requests last. Using the priority request header does not change the limits.

However, in my test setup, both high priority requests and low priority requests are being throttled equally.

I would like to know the details for the following:

1. Is the priority request headers applicable for only few set of APIs?
2. If it is applicable for every API, what is the scenario in which I can validate the difference by setting the priority?